OBJECTIVES Intracardiac echocardiography(ICE) has excellent imaging resolution and border recognition which increase strain measurement accuracy.We hypothesized that left atrial(LA) substrate and functional impairment can be detected by measuring LA strain deformation in patients with persistent and paroxysmalatrial fibrillation(AF), as compared to those with noAF.Strain deformation changes in LA and left ventricle(LV) can alsobe assessed post-ablation to determine its effect. METHODS ICE-derived speckle tracking strain(STS) was prospectively performed in 96 patients, including 62 patients with AF(31 persistent and 31 paroxysmalAF)pre-/post-ablation, and 34 patients with noAF.We measuredmajorstrain parameters including longitudinal segmental(endo/myocardial) “average peak overall strain of all segments”(PkAll), peak strain rate(SR),and different time-to-peakstrainin LA and LV images. RESULTS At baseline, persistentAFpatients had significantly lower(p<0.01) LA endocardial(4.3±2.5 vs. 20.3±8.9 and 25.5±12.9 %) and myocardial PkAll(4.4±2.6 vs. 15.7±7.2 and 20.9±9.2 %), endocardial(0.9±0.4 vs. 1.8±0.7and 2.2±0.6 1/s) and myocardial peak SR(0.7±0.4 vs. 1.5±0.6and 1.9±0.5 1/s), as compared to paroxysmal AFand noAF patients.After successful ablation,endo-/myocardial LAPkAllandpeak SR were significantly improved, most dramatically in patients with persistent AF. LV endocardial/myocardial strainand SR alsoimproved in AFpatients post-ablation. CONCLUSION LAlongitudinal strain(%)/SR(1/s) parameters in AF patientsare more abnormal than those with noAF, suggesting LA substrate/functional damage. AF ablationimprovedLAstrains/SRbut with values in paroxysmal > persistent AFsuggesting background LA damage in persistent AF.